1. Field of the Invention
This invention relates to multi-spindle CNC machine tools and, more particularly, to such a machine and machining with simultaneous synchronized cutting of all the spindles.
2. Discussion of the Background Art
Very large multi-spindle machine tools, e.g. profilers used in the aircraft industry, have large translatable gantries supporting multiple spindle carriers. Each of the carriers contains an electric motor to power the spindle and a cutting tool mounted to an end of the spindle. One such a machine is known as a rail-type five-axis gantry CNC vertical profiling machine, commercially manufactured by Cincinnati Machine, assignee of this invention, (formerly by Cincinnati Milacron, Inc). This type of machine is used to sculpt very long workpieces with the cutting tools held in three or more spindle carriers moving under command of a computer control. The spindle carriers are supported for vertical movement on a slide which, in turn, moves transversely with respect to the bed on the ways of a movable bridge or gantry slide. The gantry slide moves horizontally along the length of the bed on parallel rails mounted to the floor. A typical bed length being in the magnitude of forty to fifty feet, and the motorized spindle head, which drives multiple spindles and cutting tools, traverses the full length of the bed.
Generally, multi-spindle machines do not have spindle speed control interaction between spindles. Slight variation in speed from one spindle to the next results in a processing of the cutting teeth relative to each other. This results in a variation in phasing of the teeth and thus an adding of forces and torques and subtracting of forces and torques with respect to time. The forces and torques are reacted from the cutters, back through the spindles, the spindle carriers, and the gantry. The variation can result in poor finish and when forces combine at maximum they may induce chatter or excessive deflection. The cyclic nature of the variation causes vibrations that results in increased wear and a more rapid onset of a misalignment condition of the machine. The maximum amount of additive forces and torques occurs when all of the cutting edges engage workpieces simultaneously.